Manual controls or handles made of insulating material are used in electrical surgical instruments. The manual control carries a metal electrode on one end. The electrode is connected with a high frequency generator through a cable inserted at the other end of the manual control. The manual control is provided with one or two finger switches so that the surgeon guiding the manual control can connect the high frequency voltage or can switch between operations, for instance, of cutting and coagulation. Switches of this type, however, are required not only in such manual controls, but also used, for example, in the case of surgical instruments for minimally invasive surgery.
Since such surgical instruments are washed and sterilized with water vapor following use, the switches are installed in an insulated housing. The housing guarantees the safety of patients and surgeons, and prevents any penetrating leakage of water.
Such a housing also incorporates a conventional switch of the type disclosed in U.S. Pat. No. 3,911,241. That switch uses a fixed contact element common to both switches and two flat spring-like movable contact elements. When no operational force is exerted on the movable contact elements, they are held by two insulating bodies mounted on their end segments at some distance from the fixed contact element. Each of the surface areas of the insulated housing aligned with the movable contact elements forms an elastically deformable diaphragm. Through those areas, the movable contact elements can be bent down against the fixed contact element far enough to contact it.
Disadvantageously, the two switches can be connected simultaneously. Additionally, the plastics used for the insulated housing, such as silicon rubber or thermoplastic elastomers, cannot prevent gas diffusion into the interior of the housing at the temperature at which the sterilization occurs. Since the insulated housing is compressed by the pressure of the water vapor in the areas of the two diaphragms, such pressure closes the contacts of both switches. Following the sterilization and cooling, a very long time can be required until both switches are again opened and again able to function, since with this arrangement the diffusion processes run for considerably longer and the pressure differential is lower than during the sterilization.